1. Field of the Invention
The present invention relates to electronic watermarking, more particularly to a data processing method, apparatus, and system for adding an electronic watermark to color image data.
2. Description of the Related Art
Hardcopy documents created by word processing software, spreadsheet software, and the like are conventionally printed as binary data, that is, as digital image data. To prevent unauthorized alteration, misappropriation, and unauthorized disclosure of such digital image data, data processing methods that embed electronic watermarks in the image data have been proposed.
Electronic watermarking is not a simple matter. One problem is that the amount of electronic watermark data that can be correctly read from a watermarked image varies depending on the content of the image. In many cases the error rate in reading the watermark data also varies depending on the location at which the watermark is embedded in the image.
Digital image data generally include redundancy that cannot be visually perceived; electronic watermarks are particularly effective when they are embedded in the redundant part of the digital image data and are not perceptible to human vision. Japanese Patent Application Publication No. 2004-289783 proposes one method aimed at such embedding, but this publication contemplates only monochrome images and its method cannot be easily applied to color images.